Display screen or portion thereof with a transitional graphical user interface



FIG. 1 is a front view of a first image of a display screen or portion thereof with a transitional graphical user interface;

FIG. 2 is a front view of a second image thereof;

FIG. 3 is a front view of a third image thereof;

FIG. 4 is a front view of a fourth image thereof; and,

FIG. 5 is a front view of a fifth image thereof.

The broken line showing of the display screen, or any other portion of the figures, is included for the purpose of illustrating environment and forms no part of the claimed design.

The appearance of the image transitions sequentially between the images shown in FIGS. 1 to 5. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a transitional graphical user interface, as shown and described. 